1. Field of the Invention
This invention relates to a flame retardant epoxy resin composition which is suitable for semiconductor encapsulation and when cured, meets the flame retardance rating UL-94 V-0 without a need for flame retardants and remains stable at high temperature. It also relates to a semiconductor device encapsulated with the composition.
2. Prior Art
With the advance of semiconductor devices toward higher density, surface mount packages now become the mainstream in; the semiconductor technology. Surface mount packages are exposed to high temperatures of 215 to 260.degree. C. during mounting. Packages encapsulated with conventional encapsulants have the problems that separation can occur at the chip-encapsulant interface and cracks generate in the encapsulant portion. Thus reliability after mounting is not insured.
Under the circumstances, encapsulants comprising biphenyl type epoxy resins featuring low moisture absorption and reflow crack resistance are widely employed in these years.
As compared with the conventional encapsulants, these encapsulants comprising biphenyl type epoxy resins are superior in reflow crack resistance owing to low moisture absorption and low modulus at high temperature, but inferior in reliability tests such as a high-temperature residence test because of their extremely low glass transition temperature.
Defects are induced by high-temperature residence because intermetallic compounds form at the joints between aluminum electrodes and gold wires of IC during high-temperature residence. This results in an increased resistance and eventually the breakage of wires. It is known that the formation of such intermetallic compounds is accelerated by the presence of Br.sup.- and Sb.sup.3+ in the resin composition as a flame retardant. It is a common practice to use a combination of a brominated epoxy resin and antimony trioxide as the flame retardant.
This indicates that the high-temperature capabilities are improved if the flame retardant is omitted. Conventional formulations, however, cannot meet certain flame retardant standards, for example, the rating V-0 of Underwriter's Laboratories UL-94 unless the flame retardant is added.